Centrifugal filters may be used to separate biological substances such as an antibody enzyme, nucleic acid and protein for the purpose of concentration, desalting, purification, and fractionation. These devices are most commonly used in centrifugal-separator instruments, which may consist of a fixed-angle-rotor configuration or a swing- or variable-angle-rotor configuration. The speed of the filtering process and the recovery of retentate sample are highly valued by customers. Sample recovery values higher than 85% are usually obtained by removing the membrane capsule (sample holder) and reverse spinning it in a receiver tube.
Such devices are typically used to concentrate urine, serum, plasma and cerebrospinal fluid. For example, the measurement of specific proteins in urine can be important for the diagnosis and management of various disease states, yet the content of these proteins in urine is often too small to be detected without first concentrating the proteins. Conventional devices generally include a housing having a sample reservoir, a filter sealed in the housing so that the sample must past through the filter when subject to a driving force (such as centrifugation), and a collection chamber for collecting the concentrated sample.
Examples of some of the devices that are commercially available include Microcon™-type devices available from Millipore Corporation, in which a circular membrane is die-cut, positioned, and clamped in place using a silicone gasket. Ultrafree™-type devices are also commercially available, in which a rectangular membrane die-cut, positioned, and adhesively bonded in place. An underdrain sleeve is press fitted in place to secure the membrane in place. However, the sleeves may crack and leak, which may be caused by stresses that occur at the knit line.
Another representative device is disclosed in U.S. Pat. No. 5,647,990 to Vassarotti. Vassarotti discloses a centrifugal filter device wherein the filter is arranged in a sidewall of the filtration chamber, and a concentrate pocket is arranged in a bottom wall of the filtration chamber. Upon the application of centrifugal force, a force vector is created acting on the macromolecules in the sample and sweeping the filter surface, the causing the macromolecules to be collected in the concentrate pocket away from the filter surface.
Still another representative device is shown in U.S. Pat. No. 4,722,792 to Miyagi et al., which discloses a centrifugal filter wherein a filter film is disposed between a sample chamber and a filter chamber in a inclined or parallel manner to an axis of the filter so that regardless of whether the filter is used in an angle rotor type or swing rotor type centrifuge, the filter is positioned, during operation, so as to be inclined or parallel to the centrifugal force to reduce clogging.
However, conventional devices suffer from various drawbacks, including lower than desired recovery, filtration speed, and/or high price. It would be desirable to provide a filtration device, such as a centrifugal filtration devices, that provides improved recovery and fast filtration times at a competitive price.